assume cs:code

code segment
    start:mov ax, 0
          mov es, ax
          mov di, 200h

          mov ax, cs
          mov ds, ax
          mov si, offset captial
          mov cx, offset captial_end - offset captial
          cld
          rep movsb

          mov ax, 0
          mov es, ax
          mov word ptr es:[7ch*4], 200h
          mov word ptr es:[7ch*4+2], 0
          
          mov ax, 4c00h
          int 21h

  captial:push si
          push cx
        s:mov ch, 0
          mov cl, [si]
          jcxz ok
          and byte ptr [si], 11011111B
          inc si
          jmp short s

    ok : pop cx
         pop si
         iret
captial_end: nop

code ends
end start


